I want to install a 1" garboard drain and would like advice on the best bit type for this. I have an Irwin Speedbor 3 blade and a 1" hole saw.

Hole saws work much better on fiberglass than a speedbor. I try to use the bi-metal hole saws as they stand up a bit better than regular steel to fiberglass, and it's likely the saw will require sharpening after running it through the glass.

Also - drill part way through the glass, and when the center drill pokes out the other side stop cutting, move to the other side and finish the hole from there - you'll get a finished edge on both sides of the hole.

Thanks guys. I drilled the hole with the hole saw, took my time and it went smooth. I could not go to the opposite side since its down at the bottom of the bilge though. It appears to not be ripped badly. Thanks again.

If any one else is doing this you might consider trying carbide abrasive hole saws for fiberglass. A regular hole saw can rip fibers out around the cut even on the start side of the cut, and as was mentioned the blowout on the back side of the cut can be ugly. Gel coat chipping around the initial cut is pretty common too, especially with a dull hole saw. Abrasive saws solve all this and should be standard gear in a really good boat shop, IMHO.